The present invention relates to an apparatus for and a method of displaying sequential processing, and more particularly to a display apparatus and a display method suitable for use in the case where sequential processing is displayed on the display surface of a cathode ray tube by logic symbols.
There have been widely employed sequential control devices in which signals are supplied to a controlled system in a predetermined order to control the system. In recent years, most sequential control devices have been designed to include a digital computer for conducting sequential control. That is, such devices perform logical operations on the basis of a program. Accordingly, the sequential control devices are required, from the user's side, to be designed such that the contents of sequential processing can be readily modified by an operator who is skilled in sequential control techniques but lacks the knowledge of digital computers and programming. To satisfy the above requirement, a sequence display control unit including a CRT control unit having a CRT for providing a display on the display surface of the CRT are added to the sequential control device for achieving appropriate display of the sequence control.
The sequence display control unit is a sort of language compiler, which converts sequence symbols inputted through a key-in operation into programs and simultaneously displays sequence symbols corresponding to the programs on the display surface of a cathode ray tube through the CRT control unit. Therefore, an operator can design a desired sequence control while observing a corresponding logical circuit diagram displayed on the display surface of the cathode ray tube. When the logical circuit diagram thus formed is a satisfactory one, keying-in the consent approval of the diagram will store the programs corresponding to such a series of logical circuits in the sequential control device and subsequent control operations on the controlled system are performed on the basis of the newly formed programs.
The present invention relates to display of a logical circuit on the display surface of a cathode ray tube in such a sequence display control device. In a conventional system, a ladder display has been employed in which a bus bar is displayed at each end of the display surface, and symbols of contacts are arranged in series or parallel between the above bus bars. The ladder display system has been widely employed, but is not suited to display complicated circuits.